1. Field of the Invention
The present invention relates to a printer-control method and a printer-control apparatus, and in particular, to a printer-control method and a printer-control apparatus that in a paper-supply operation into a printer, speed control of a paper-supply motor is performed when a printing paper abuts against a paper-feed roller and a driven roller and is nipped by them. Further, the present invention relates to a storage medium which stores a computer program for executing the printer-control method.
2. Related Background Art
FIG. 1 is an explanatory illustration typically showing structures of components that relate to paper-supply of printing paper and detection of upper and lower ends of the printing paper in a printer.
In the printer, as shown in FIG. 1, printing papers 50 that are set in a tray 90 are fed one by one by a paper-supply roller 64. Then, an upper end of the printing paper 50 is detected by a paper sensor 15. A paper-supply motor 63 (see FIG. 10) is coupled to the paper-supply roller 64. The paper-supply roller 64 is driven by driving and controlling the paper-supply motor 63 and thus the paper is supplied into the printer.
Then, the printing paper 50 is fed by a paper-feed roller 65 and a driven roller 66. Printing is performed on a platen 84 by an ink discharged from a printhead 9. Printing advances to a vicinity of a lower end of the printing paper 50 while the printing paper 50 is successively fed. The printing paper 50 does not exist on the paper sensor 15 at a certain time. In this way, the lower end of the printing paper 50 is detected.
An operation of supplying a printing paper into a printer is generally performed as described above. In the paper-supply operation, when a printing paper abuts against a paper-feed roller and a driven roller and is nipped therebetween, i.e., at a time of so-called abutting and nipping, the upper end of the printing paper is desirably nipped between the paper-feed roller and the driven roller so as to be parallel to them.
In actuality, however, when the printing paper abuts the paper-feed roller and the driven roller and is nipped therebetween, the upper end of the printing paper is not perfectly parallel to the paper-feed roller and the driven roller. The upper end of the printing paper is often nipped while slightly inclined.
Then, after the printing paper is nipped, the printing paper which is nipped by the paper-feed roller and the driven roller is fed in a reverse direction and pushed back, i.e., discharging of the printing paper is performed. By repeating such nipping and discharging for several times, the upper end of the printing paper is perfectly parallel to the paper-feed roller and the driven roller. In this way, deskew of the printing paper is performed. Deskew operation of printing paper will be hereinafter described in detail with reference to the drawings.
FIGS. 2A through 2E are explanatory illustrations typically showing states of the paper-supply roller, the paper-feed roller and the printing paper in deskew of the printing paper, seen from the side. FIGS. 3A through 3E are explanatory illustrations typically showing states of the paper-supply roller, the paper-feed roller and the printing paper in deskew of the printing paper, seen from above.
As shown in FIGS. 2A and 3A, when each printing paper 50 is fed by the paper-supply roller 64 one by one, in accordance with rotational operation of the paper-supply roller 64, an upper end of the printing paper 50 gradually approaches the paper-feed roller 65 and the driven roller 66. At this time, the upper end of the printing paper 50 is desirably parallel to the paper-feed roller 65 and the driven roller 66. As shown in FIG. 3A, however, the upper end of the printing paper 50 may be inclined with respect to the paper-feed roller and the driven roller.
As shown in FIGS. 2B and 3B, when the paper-supply roller 64 is further rotated, the upper end portion of the printing paper 50 abuts against the paper-feed roller 65 and the driven roller 66 and is nipped therebetween. As described above, such state is referred to as nipping of the printing paper.
The paper-supply roller 64 is rotated by a predetermined amount and then stopped in order to deskew the printing paper. At this time, a length of the upper end portion of the printing paper which is extended off from the position at which the printing paper 50 is nipped by the paper-feed roller 65 and the driven roller 66 toward the printer is referred to as a nipping amount C. The nipping amount C is usually set for each type of the printing paper 50 and can be changed by setting a printer corresponding to the type of the printing paper 50. Referring to FIGS. 2B and 3B, the state in which the printing paper 50 abuts against the paper-feed roller 65 and the driven roller 66 while being inclined is shown. Thus, the nipping amount C shows a nipping amount at a generally central portion of the printing paper 50.
Then, as shown in FIGS. 2C and 3C, in order to deskew the printing paper 50, the paper-feed roller 65 is rotated in reverse while the paper-supply roller 64 is stopped. The printing paper 50 is fed in reverse by the nipping amount C and thus discharged. The printing paper 50 which is fed in reverse by the nipping amount C and discharged is deflected. Further, the upper end of the printing paper 50 is forcibly abutted against the paper-feed roller 65 and the driven roller 66 because of flexibility of the printing paper itself. At this time, the upper end of the printing paper 50 is generally parallel to the paper-feed roller 65 and the driven roller 66.
When the upper end of the printing paper 50 is generally parallel to the paper-feed roller 65 and the driven roller 66, as shown in FIGS. 2D and 3D, the paper-feed roller 65 is rotated forward within a range of the nipping amount C, so that the upper end of the printing paper 50 is nipped by the paper-feed roller 65 and the driven roller 66. Then, by repeating nipping shown in FIGS. 2D and 3D and discharging shown in FIGS. 2C and 3C for several times, the upper end of the printing paper 50 becomes parallel to the paper-feed roller 65 and the driven roller 66.
When the upper end of the printing paper 50 becomes parallel to the paper-feed roller 65 and the driven roller 66, the paper-feed roller 65 is rotated forward and the printing paper 50 is nipped again by the paper-feed roller 65 and the driven roller 66. Further, the paper-supply roller 64 is rotated such that the printing paper 50 is released. Thereafter, subsequent paper-feed operation is performed. In this way, deskew of printing paper is performed.
Next, a description will be given about speed control of the paper-supply motor from the time when a paper-supply roller starts a paper-supply operation to the time when the paper-supply roller is stopped to deskew a printing paper.
FIG. 4 is a graph showing a first example of target speed, current speed and waveform of control signal for the paper-supply motor from the time when a paper-supply roller starts a paper-supply operation to the time when the paper-supply roller is stopped in order to deskew a printing paper. FIG. 5 is a graph showing a section from 300 to 0 of remaining distance to a target stop position shown in FIG. 4 with only a horizontal axis being enlarged.
The target stop position shown in FIGS. 4 and 5 show a position at which an upper end of printing paper is nipped by the paper-feed roller 65 and the driven roller 66 by a predetermined nipping amount C and the paper-supply roller 64 is stopped in order to deskew the printing paper.
At a section from 800 ({fraction (1/1440)} inches (1 inch=2.54 cm): a unit will be appropriately omitted hereinafter) to 700 of remaining distance to the target stop position, a PID waveform is shown. Nevertheless, this section is not a PID control section but an acceleration control section. At the section, acceleration toward a target speed Vref in a constant speed section from 700 to 300 of remaining distance is performed.
In the constant speed section from 700 to 300 of remaining distance, PID control starts. Thereafter, the PID control is performed until the paper-supply motor is stopped in order to stop the paper-supply roller 64 at the target stop position. At the constant speed section, the PID control is performed so as to converge undershoot and overshoot of current speed Vcur relative to the target speed Vref.
Speed reduction control of the target speed Vref gradually starts at the remaining distance of about 300 and more rapid speed reduction control is performed from 200 of remaining distance.
Undershoot of the current speed Vcur occurs at 200 to 100 of remaining distance in the speed reduction control section. This is because the upper end of printing paper abuts the paper-feed roller 65 and the driven roller 66 and thus the current speed Vcur is temporarily and rapidly reduced.
Since the PID control is performed at the speed reduction control section, in order to reduce a difference between the target speed Vref and the current speed Vcur in an undershoot section, a PID command value for instructing acceleration is outputted.
However, while the paper-supply motor is accelerated in accordance with the PID command value, the target speed Verf is reducing. Thus, overshoot of the current speed Vcur occurs at a section from 100 to 20 of remaining distance by contraries.
Then, in order to reduce a difference between the target speed Vref and the current speed Vcur in the overshoot section, a PID command value for instructing reduction in speed is outputted by the PID control.
As a result, although overshoot of the current speed Vcur is converged at around 20 of remaining distance, undershoot of the current speed Vcur occurs again at a section from 20 to 5 of remaining distance.
In order to reduce a difference between the target speed Vref and the current speed Vcur in the undershoot section, a PID command value for instructing acceleration is outputted and thus the current speed Vcur generally coincides the target speed Vref. Then, a PID command value for instructing reduction in speed in accordance with the target speed Vref is outputted. At the target stop position, the current speed Vcur becomes 0 and the paper-supply motor and the paper-supply roller stop.
For control of the current speed Vcur of the paper-supply motor under the above-described PID control, output pulses of two phases, i.e., A phase and B phase of encoder are used. Nevertheless, both output pulses of two phases of the encoder are not always used but used depending on a control section. Namely, in the constant speed section from 700 to 300 of remaining distance, because a speed of motor is sufficiently high, both output pulses of two phases of encoder are not required. For example, only a rising edge of output pulse of A phase of the encoder is used and an interruption of speed control calculation is generated. In the speed reduction section from 300 to 0 of remaining distance, a speed of motor is reduced toward 0 and more precise speed control is required. Thus, an interruption of speed control calculation is generated by using rising and falling edges of each of the output pulses of A phase and B phase of the encoder.
Setting of proportional gain coefficient used for speed control calculation under PID control in the constant speed section is usually different from that of the speed reduction section. If the proportional gain coefficient is set to be too large in the constant speed section, vibration and unpleasant noise are often generated due to resonance of a driving force transmitting mechanism. Thus, the proportional gain coefficient is set to be relatively so small that generation of vibration and unpleasant noise is prevented. On the other hand, the proportional gain coefficient is set, in an ordinary state, to be the same as in the constant speed section because of the same reason. Nevertheless, in the speed reduction section, as undershoot and overshoot due to abutment of printing paper occur, a variation in speed that is more sever than that of the constant speed section must be rapidly converged. Accordingly, if a difference between the target speed Vref and the current speed Vcur exceeds a predetermined threshold, the proportional gain coefficient is set to be changed to a larger value than an usual value.
Speed control of the paper-supply motor from the time when a paper-supply roller starts a paper-supply operation to the time when the paper-supply roller is stopped in order to deskew a printing paper is described above. Timings that undershoot and overshoot of current speed Vcur are generated by an upper end of printing paper abutting against the paper-feed roller 65 and the driven roller 66 are varied depending on a set value of the nipping amount C of printing paper. A size or a duration of the undershoot and the overshoot is varied depending on a type of the printing paper or an angle of the upper end of the printing paper with respect to the paper-feed roller and the driven roller.
When the upper end of the printing paper abuts against the paper-feed roller 65 and the driven roller 66 at the speed reduction section, a proportional gain coefficient used for speed control calculation is changed to a larger value in accordance with generation of undershoot of the current speed Vcur with respect to the target speed Vref. Thus, undershoot and overshoot due to abutment of the printing paper can be usually converged such that problems do not occur at subsequent operations.
When an initial nipping amount C at a time of deskew operation for printing paper is set to be large, the upper end of the printing paper may abut against the paper-feed roller 65 and the driven roller 66 at the constant speed section.
A proportional gain coefficient used for speed control calculation in the constant speed section is determined by presupposing that a variation width of the current speed Vcur is small. Further, the proportional gain coefficient is always set to be a relatively small certain value in order to prevent generation of aforementioned vibration and unpleasant noise. The proportional gain coefficient is not changed to a value larger than an usual value regardless of a difference between the target speed Vref and the current speed Vcur.
Accordingly, in the case where abutment of printing paper occurs at the constant speed section, undershoot and overshoot of the current speed Vcur with respect to the target speed Vref caused by abutment of the printing paper cannot be converged such that problems do not occur at subsequent operations. There arises a problem in that depending on a size or a duration of undershoot and overshoot, the current speed Vcur may become 0 before reaching the target stop position, and the paper-supply motor and a printing paper stop on their ways. As a result, subsequent deskew operation for printing paper may be hindered.
An object of the present invention is to provide a printer-control method and a printer-control apparatus that are configured such that in speed control of the paper-supply motor from the time when a paper-supply roller starts a paper-supply operation to the time when the paper-supply roller is stopped in order to deskew a printing paper, i.e., to the time when the paper-supply roller is stopped while an upper end portion of the printing paper is nipped by a paper-feed roller and a driven roller thereof, undershoot and overshoot of speed waveform of the paper-supply motor caused by abutment of the upper end of the printing paper against the paper-feed roller and the driven roller can be converged as soon as possible and stop of the printing paper on its way caused by such undershoot and overshoot can be prevented.
According to the printer-control method of the present invention, there is provided with a printer-control method in speed control for a paper-supply motor from the time when a paper-supply roller starts a paper-supply operation to the time when an upper end of a printing paper abuts against a paper-feed roller and a driven roller thereof and then the paper-supply motor is stopped with the upper end portion of the printing paper being nipped by the paper-feed roller and the driven roller thereof, when a difference between a target speed and a current speed in a constant speed section under feedback control becomes equal to or larger than a predetermined value, a proportional gain coefficient used for speed control calculation is changed to a value which is larger than an usual value.
In the above configuration of the printer-control method according to the present invention, control for changing the proportional gain coefficient can be performed on the condition that a nipping amount of the printing paper with respect to the paper-feed roller and the driven roller thereof at a target stop position at which the paper-supply motor is stopped with the upper end portion of the printing paper being nipped by the paper-feed roller and the driven roller thereof is set to be equal to or larger than a predetermined value.
According to the printer-control apparatus of the present invention, there is provided with a printer-control apparatus comprising a feedback control component which changes a proportional gain coefficient used for speed control calculation to a value which is larger than an usual value when a difference between a target speed and a current speed in a constant speed section under feedback control becomes equal to or larger than a predetermined value in speed control for the paper-supply motor from the time when a paper-supply roller starts a paper-supply operation to the time when an upper end of a printing paper abuts against a paper-feed roller and a driven roller thereof and then the paper-supply motor is stopped with an upper end portion of the printing paper being nipped by the paper-feed roller and the driven roller thereof.
In the above configuration of the printer-control apparatus according to the present invention, the feedback control component can perform control for changing the proportional gain coefficient on the condition that a nipping amount of the printing paper with respect to the paper-feed roller and the driven roller thereof at a target stop position at which the paper-supply motor is stopped with the upper end portion of the printing paper being nipped by the paper-feed roller and the driven roller thereof is set to be equal to or larger than a predetermined value.
Furthermore, in the above configuration of the printer-control method and the printer-control apparatus according to the present invention, the predetermined value of the nipping amount is a minimum value of the nipping amount in the case where the printing paper abuts against the paper-feed roller and the driven roller thereof in the constant speed section under feedback control.
In accordance with a printer-control method and a printer-control apparatus according to the present invention, because of the above-described structure, undershoot and overshoot of current speed relative to target speed due to abutment of upper end of printing paper against a paper-feed roller and a driven roller thereof can be rapidly and appropriately converged. As a result, it is possible to prevent the printing paper from stopping on its way caused by such undershoot and overshoot.
A storage medium according to the present invention stores a computer program for executing any of the printer-control methods of the present invention on a computer system.